When you develop a sinus infection or some other inflammatory disorder that causes coughing due to post-nasal drip, the mucus that is continually produced by the cells lining your sinus passages drips down your throat and nose. This not only causes the coughing spasms associated with post-nasal drip, it also coats the back of your throat and the back of your tongue with mucus. When the mucus is thick and just sits there in your throat and on the back of your tongue it not only smells bad, it is in the perfect dark, warm, moist environment that breeds the bacteria that causes halitosis.
This whole process could be started by an allergy, a sinus infection, a non-infectious inflammation of the sinuses or even chronic sinusitis. Sometimes this can be treated by your regular over-the-counter medications but any condition that lasts over two weeks should signal the need for a doctor visit.
If you can do something to reduce or eliminate the mucus, you will be reducing or eliminating the bad breath associated with the mucus. Some things you can do are:
Cut down on dairy products: All dairy products have some fat content. This fat content can make the existing mucus thicker, worsen your cough and exacerbate your halitosis. Try switching to low-fat milk, low-fat cottage cheese, low-fat cheeses, and etc. This won't help to cure your sinus problem, but it will help to reduce the resulting cough and bad breath.
Drink lots of water: Drinking lots of water is a great habit to get into. Drinking six to eight eight-ounce glasses of water every day will help to thin out the mucus caused by a sinus condition and will reduce the cough and reduce the bad breath. Even if you aren't bothered by a cough, drinking this much water on a regular, daily basis will keep your mouth, tongue and throat cleaner and wash away some of the bacteria that causes bad breath.
Avoid caffeine and alcohol: This is especially important when you have a sinus problem that is causing a mucus buildup. Avoid drinking any caffeinated or alcoholic beverages. The caffeine and alcohol will only make the problem worse.
No smoking please: Understandably, smoking has a negative effect on your sinuses (and on your entire respiratory system). Anything that irritates the sinuses will contribute to the mucus buildup in your throat and on the back of your tongue and will make your cough and bad breath worse. If you are a smoker, the time-period surrounding your sinus problems is a great time to make another effort to quit. or at least make a genuine effort to cut back while your sinuses are on their rampage.
Nasal wash: A solution that will help to remove mucus and germs from your nose and sinuses is your best option for reducing postnasal drip and its associated mucus, coughing and halitosis.
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You can see your doctor or pharmacist for a recommended nasal wash solution or you can make your own -- here's a recipe.
Homemade saltwater nasal wash solution
Note: make a fresh solution in a clean glass for every use, don't save any leftover solution.
What you need:
A clean glass
8-ozs of water (use bottled water if you can -- it has fewer impurities)
1/2 tsp. of uniodized salt (Uniodized salt is recommended because it is less irritating than iodized salt is to your nasal passages and it works just as well.
A large, rubber ear syringe.
Thoroughly mix 1/2 teaspoon of un-iodized salt in an 8-oz glass of water
Add just a pinch of baking soda and stir it in the saltwater.
Fill the syringe with the salt-water solution.
Insert the syringe in one nostril and squeeze gently but with enough pressure to get the solution all the way into the sinus cavity.
Repeat for the other nostril.
Gently blow your nose.
This should be a daily procedure while the sinus problem exists. It is best to use the entire 8-ozs of solution each time you perform this procedure. If you don't use it all, remember to throw away the remaining solution and prepare a fresh batch for the next application.
If this solution doesn't work to your satisfaction, consult your doctor to make sure there isn't some other problem and ask him or her about using a steroid nasal spray for your condition.